1. Field of the Invention
The present invention in one embodiment relates to an electroconductive polymer having a high stability and exhibiting high solubility in water and also relates to a process for producing the polymer. More specifically, the present invention in this embodiment relates to a water-soluble electroconductive polymer particularly suitable for use as electrodes, sensors, electronic display elements, nonlinear optical elements, photoelectric conversion elements, antistatic agents, conducting materials, and optical materials which require high workability in the field of electric and electronic industry and a process for producing the polymer.
The present invention in another embodiment relates to an extremely stable electroconductive polymer having high solvent solubility and to a process for producing the polymer. More specifically, the present invention relates to the polymer and to a process for producing an electroconductive polymer particularly suitable as an electrode, a sensor, an electronics display element, a non-linear optical element, a photoelectric conversion element, or an antistatic agent, which encounters severe processability requirements in the field of electric and electronic industries, as well as being suitable for various electroconductive or optical materials.
2. Description of the Related Art
Polymers of an advanced .pi. electron conjugate system have attracted attention in industries concerned due to their characteristics such as not only conductivity but also behavior manifested in the change of state during the metal/semiconductor transition. Thus, studies have been made with a view to developing these polymers suitable for varying applications. Among other polymers of this class, water-soluble self-doping conjugate type polymers which are obtained by having a Bronsted acid group joined to the main chain of polymer by covalent bond either directly or indirectly with the aid of a spacer have arrested a particular interest in respect that they possess stable electroconductivity over a long period without needing contribution of any external dopant.
Specific examples thereof include a polythiophene derivative having an alkanesulfonic acid group (F. Wudl et al., Journal of American Chemical Society, vol. 109, p. 1858, 1987; and E. E. Havinga et al., Polymer Bulletin, vol. 18, p. 277, 1987), a polythiophene derivative or a polypyrrole derivative (Aldissi, U.S. Pat. No. 4,880,508), a polymer having an alkanesulfonic acid group or an alkylcarboxyl acid group as a substituent in an aromatic ring of polyaniline (WO 87/05914; JP-A-63-39916), a polymer having a propanesulfonic acid group substituted at the N-position of pyrrole (J. Chem. Soc., Chemical Communication, p. 621, 1987), a polyaniline derivative having a propanesulfonic acid group substituted at the N-position (J. Chem. Soc., Chemical Communication, p. 180, 1990 and Synthetic Metals, vol. 31, p. 369, 1989), a polyaniline derivative having a sulfonic acid group substituted directly on the aromatic ring (J. Am. Chem. Soc., vol. 112, p. 2800, 1990), and a polycarbazole derivative having an alkanesulfonic acid group substituted at the N-position (U.S. Pat. No. 5,130,412). In addition, their production processes are also disclosed in these publications.
Furthermore, an oxidative chemical polymerization of a thiophene derivative monomer having an alkanesulfonic acid group is disclosed in JP-A-2-189333.
Further, among condensed heteropolycyclic compounds, isothianaphthene, benzo[c]furan, and naphtho[2,3-c]thiophene, each having a .pi.-conjugated quinoid structure, are known to have a very high reactivity, and require specific procedures for their isolation (see, J. Org. Chem., vol. 36, p. 3932, 1971, and Recl. Trav. Chim. Pays-Bas, vol. 87, p. 1006, 1968).
As a specified example of bicyclic conducting polymers, polyisothianaphthene is disclosed in conjunction with a method for the production thereof in J. Org. Chem., 49, 3382 (1984), in which it is described to possess a stable conductivity as evidenced by an extremely small energy gap of 1.1 eV. However, polyisothianaphthene is neither soluble nor fusible and is extremely deficient in moldability. A method for rendering this particular polymer soluble in an organic solvent by introducing an alkyl group or alkoxy group into the polymer is disclosed in JP-A-2-242816. The term "JP-A" as used herein means an "unexamined published Japanese patent application".
The thought that the conductivity of such isothianaphthene polymers is further influenced by introducing an electron attracting or donating group into the isothianaphthene backbone has been reported in conjunction with results of calculation by Bredas et al. in J. Chem. Phys., 85(8)., 4673 (1986). As examples of the polymers relating to such isothianaphthene polymers, polymers having a halogen atom as a substituent as disclosed in JP-A-63-307604 and polymeric compounds possessing an isothianaphthene backbone having an electron attracting group as a substituent as described in JP-A-02-252727 may be cited. A process for producing a polymer having a naphtho[2,3-c]thiophene structure, which is a heterotricyclic electroconductive polymer that is neither soluble nor fusible, has been reported in Synthetic Metals, vol. 35, p. 263, 1990. The oxidative chemical polymerization of 1,3-dihydroisothianaphthene without a sulfonic acid group is disclosed, for example, in JP-A-63-118323 and U.S. Pat. No. 4,789,748. Bicyclic water-soluble conducting polymers, having an isothianaphthenylene structure, an isobenzofurylene structure, an isoindolylene structure, an isobenzoselenylene structure, or an isobenzotellurylene structure as a repeating unit thereof, have never been disclosed to the art to date. Neither of these patent publications has any specific disclosure of the polymer having a sulfonic acid group on repeating unit of the present invention nor of a method for the production of such a polymer.